Small, segmented creatures that curl into a tight ball when disturbed are a common sight in gardens and damp areas. Many people refer to them as “rolly pollies.” A frequent question arises: are rolly pollies a type of millipede? This question highlights a widespread misunderstanding about these distinct creatures.
Are Rolly Pollies Millipedes?
Rolly pollies are not millipedes. Despite their similar appearance and shared habitat preferences, these two groups of arthropods belong to entirely different biological classifications. Rolly pollies are terrestrial crustaceans. In contrast, millipedes are myriapods, belonging to the Class Diplopoda. This fundamental difference in classification means they are no more related than a crab is to a centipede.
The True Identity of Rolly Pollies
Rolly pollies, also known as pill bugs, sow bugs, or woodlice, are crustaceans. This places them in the same broad group as crabs, lobsters, and shrimp. They are the only crustaceans that spend their entire lives on land, though they still require moist environments to survive.
Their bodies are oval-shaped and segmented, covered by a hard exoskeleton. They typically have seven pairs of legs, with one pair per body segment. A distinguishing feature of many rolly pollies is their ability to roll into a tight ball, a defensive behavior called conglobation. This protects their softer underside by presenting their armored shell.
They breathe using gill-like structures, which necessitates their preference for damp, dark habitats such as under rocks, logs, or leaf litter. Rolly pollies are detritivores, primarily feeding on decaying plant matter, and play a role in breaking down organic material and returning nutrients to the soil.
The World of Millipedes
Millipedes are arthropods belonging to the Class Diplopoda, part of a larger group called myriapods. The name “Diplopoda” refers to their most distinctive feature: most of their body segments have two pairs of legs. While their common name means “thousand feet,” most species have fewer than a hundred pairs of legs.
Their bodies are typically elongated and cylindrical, though some can be flattened. Millipedes are slow-moving creatures that use their many legs to push through soil and leaf litter. They are detritivores, feeding on decaying plant matter and contributing to decomposition. When threatened, millipedes do not bite; instead, they often coil into a tight spiral or ball, protecting their vulnerable underside. Many species also secrete foul-smelling or toxic compounds from glands along their bodies as a defense mechanism.